Airbag modules currently used in automobiles comprise an inflator for rapid generation of gas, activated upon rapid deceleration of the automobile as in a collision, a canister which contains the inflator and transmits gas from the inflator to the airbag, and an airbag which will be deployed and inflated by gas issuing from the inflator. The airbag, when inflated, provides a cushion in front of a vehicle occupant to arrest forward motion of the driver or passenger in a collision.
The shape of the inflated cushion will be determined primarily by the shape of walls of the airbag but may be further affected by the use of one or more tethers inside the airbag. Tethers may be used to alter the shape of an inflated cushion or for relieving excessive stress in an airbag wall at a point or line where the outer end of the tether is attached to the airbag.
Tethers may also be used for restraining or limiting the extension of the airbag at points where tethers are attached to the airbag walls. One purpose for the use of tethers is to prevent a "slapping" motion of the airbag at its outer end. When a top mounted passenger side airbag is being deployed into the passenger compartment, before it is fully inflated, the outer end of the airbag may extend outward beyond its normal reach for an instant before the airbag assumes its fully inflated shape. This may cause the outermost end to slap an occupant in the vehicle. The use of tethers can prevent such over extension at the outer end of the airbag and thus prevent such slapping of the occupant.
In many airbag constructions that use tethers, one end of the tether is anchored by attachment to the airbag fabric at or near the mouth or throat of the airbag fabric. At its other end the tether will be attached at a selected point or line to the inner wall of the airbag. A conventional means for attaching the tether inside the airbag has been to sew the tether at each of its ends to the airbag fabric wall at selected points. However, this anchoring of the one end of the tether to the area at, near or around the mouth of the airbag, such as shown in U.S. Pat. No. 5,044,663, can cause undue stress in the airbag and the airbag fabric may rip if the stress becomes too great.
U.S. Pat. No. 4,941,678 described an airbag structure in which a tether at the throat of the airbag and the airbag wall were both sewn to a band having a continuous loop which encircled a retaining ring held by the canister. The present invention has the advantage that the end of the tether itself encircles a retaining rod held to the canister so that stress in the tether is transmitted directly from the tether to the retaining rod without an intervening member encircling the retaining rod with the end of the tether held only by stitching the tether to such intervening member.
In some prior art structures the end of the airbag wall, but not the end of the tether, would extend around a retaining rod to fasten the airbag to the canister. In those constructions, stress from the tether was transmitted to the canister only through a panel of the airbag to which the end of the tether was sewn and the airbag in turn transmitted such stress to the canister.